The allergic reaction of type I, i.e. immediate, as well as in allergic reaction of type IV, i.e. delayed, according to Gell and Coombs classification, in case of skin provocation tests is accompanied by histamine release, i.e. β-Imidazol-ethanamine, what causes a local subcutaneous hyperthermia. This hyperthermia occurs due to activation of H1 receptors located on the surface of the capillary arterioles endothelium, causing their expansion and in consequence an increased blood flow. This increased blood flow provides an endogeneous heat source, revealed subcutaneously as a focal hyperthermia, and on the surface of skin as an erythema, the so-called elevated temperature erythema.
Low values of thermal conductivity coefficient of the skin cause that the effect of heat diffusion via thermal conduction from a point heat source in the location of allergen introduction can be neglected. In consequence, as disclosed in publication by Wong et al., “Minimal role for H1 and H2 histamine receptors in cutaneous thermal hyperemia to local heating in humans”, Journ. Appl Physiol., 2006, it can be assumed that the diameter of the elevated temperature area observed on the surface of the skin, i.e. the erythema, corresponds directly to the size of the heat source resulting from increased blood perfusion enforced by the histamine diffusing in the skin. This is an observed specific dermo-thermal effect resulting only from vasodilatory action of the histamine released during the allergic reaction of skin, wherein the effect is not to be associated with other accompanying patophysiological processes, in particular those induced by inflammatory mediators.
In previous methodology for reading the results of allergy provocation skin tests a subjective quantitative measure in the form of 5 point scale has been applied. In order to determine if an immediate allergic reaction to an introduced allergen has occurred, the diameter of the resulting erythema is measured ca. 15 minutes after performing the test with a ruler scaled in millimeters, as a reaction for the tested substance, next the diameter is compared to the diameter of a reference reaction to introduced histamine with concentration of 1 mg/ml and with a control test with the use of physiological saline (NaCl) solution with concentration of 0.9%.
The extent of the erythema is considered to be a qualitatively-quantitative indicator of positive result of allergy test. However, a direct visual evaluation of the skin test result is not an objective method and has a number of drawbacks coming directly from large variability of the reaction characteristics in short time intervals.
A clinical problem is precise and objective determination, based on the size of the erythema, if the examined patient, i.e. a child, an adult or an elder person.
In fact is allergic to the specific introduced allergen, since only a ruler and the examiner's eye are used for this purpose on standard basis. The scientific literature implies, that the measurable this way allergic reaction having the form of an erythema, resulting from a reaction provoked by the introduction of an allergen causing mast cells degranulation and release of histamine acting vasodilatory, if positively correlated with focally increased skin temperature from 1.5° C. to 2.5° C., wherein the surfaces of allergic reaction registered by thermographic instruments are 3 to 5 times larger than changes visually recognizable on the skin. This means that thermography allows to image the actual extent of the hyperthermia occurring subcutaneously during allergic reaction, in contrast to epidermic erythema being only a visual symptom of this hyperthermia. A thermographic device functions in this case as a converter and a thermo-optical intensifier of thermal image of the histamine reaction, and specifically the vasodilatory component of this reaction, resulting in hyperthermia generated in a cascade of processes in response to the introduced allergen.
The application of thermography enables objective determination of the actual intensity of the skin allergic response measured by the extent of the subcutaneous vascular hyperthermia, producing a colour image of temperature distribution around the allergen introduction location and on the surface of the surrounding skin and allowing for a precise measurement of the diameter of the actual hyperthermal reaction, and not its external symptom having the form of an erythema, promoting correct diagnosis. The usefulness of thermography, this time remote, by means of an infrared camera comprising a cooled bolometer and connected to a computer, recording emission of heat from the surface of the examined skin, for measuring the allergic response has been already pointed out by Bagnato et al. “Measurement of allergen-induced skin reactions by computerized dynamic telethermography”, Journ. Investig Allergol Clin Immunol., 1997. In the experiment described therein the patients have been subjected to point skin tests with the use of a set of allergens, a neutral control solution, e.g. 0.9% NaCl, as well as histamine solutions.
In the European patent application EP0189381 there is disclosed a system for acquiring thermographic images of body surface by means of a camera directed towards a liquid-crystal plate, wherein the detector system comprises a non-thermally calibrated liquid-crystal plate, therefore the transformation of the recorded image occurred due to the operation of software, what makes it impossible to precisely filter out the epidermic hyperthermia, what is necessary in dermatological diagnostics.
The solutions known in the state of the art are not suitable for application for the purposes of clinical dermatological diagnostics because of significant complication of operations to be undertaken during calibration, and also because of susceptibility to changes of thermal background temperature of the examined region of skin, what makes it impossible to precisely separate the images of the actual allergic hyperthermia from artefacts arising from the contributed thermal propagation from other epidermic changes related to the patient's health.
The object of the invention is to solve the mentioned problems.